Diaphragm and bellows pressure gauge

In this PPt u will see
1.Introduction
2.principle
3.construction
4.working
5.advantages and disadvantages
6.application
of Diaphragm and bellows pressure gauge

1. DIAPHRAGM AND BELLOWS PRESSURE GAUGE By- Krishna Kant N ayak MNIT,JAIPUR

2. Pressure MEASUREMENT Represented as force per unit area Restricted to fluids These instruments are used to measure gauge pressure. Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. What is gauge pressure? The difference between absolute pressure and atmospheric pressure is known as gauge pressure. S.I unit is Pascal i.e N/m 2/                

3. DIAPHRAGM PRESSURE GAUGE Diaphragm is a elastic material which displaces, when it is applied to pressure. The Diaphragm Pressure Gauge uses the elastic deformation of a diaphragm (i.e. membrane) instead of a liquid level to measure the difference between an unknown pressure and a reference pressure.

4. Construction and working

5. A typical Diaphragm pressure gauge contains a capsule divided by a diaphragm, as shown in the schematic . One side of the diaphragm is open to the external targeted pressure, P Ext , and the other side is connected to a known pressure, P Ref ,. The pressure difference, P Ext - P Ref , mechanically deflects the diaphragm.

6. The membrane deflection can be measured in any number of ways. For example, it can be detected via a mechanically-coupled indicating needle, an attached strain gage , a linear variable differential transformer (LVDT; see the schematic below), or with many other displacement/velocity sensors. Once known, the deflection can be converted to a pressure loading using plate theory .

7. Pros and Cons PROS- Much faster frequency response than U tubes. Good for low pressure. Higher overpressure safety. Used to measure gauge, atmospheric and differential pressure. CONS- More expensive then other pressure sensors.

8. BELLOWS PRESSURE GAUGE

9. Like a diaphragm , bellows are also used for pressure measurement , and can be made of cascaded capsules. The basic way of manufacturing bellows is by fastening together many individual diaphragms. The bellows element, basically, is a one piece expansible, collapsible and axially flexible member

10. construction For industrial purposes, the commonly used bellow elements are: By turning from a solid stock of metal By soldering or welding stamped annular rings Rolling a tube By hydraulically forming a drawn tubing.

11. For selecting a specific material for an elastic member like bellows, the parameters to be checked are: Range of pressure Hysteresis Fatigue on dynamic operation Corrosion Fabrication ease Sensitivity to fluctuating pressures

12. Working

13. The action of bending and tension operates the elastic members. For proper working, the tension should be least.As the inlet pressure to the instrument varies, the bellows will expand or contract. The moving end of the bellows is connected to a mechanical linkage assembly. As the bellows and linkage assembly moves, either an electrical signal is generated or a direct pressure indication is provided.

14. The flexibility of a metallic bellows is similar in character to that of a helical, coiled compression spring. Up to the elastic limit of the bellows, the relation between increments of load and deflection is linear. However, this relationship exists only when the bellows is under compression. It is necessary to construct the bellows such that all of the travel occurs on the compression side of the point of equilibrium.

15. Therefore, in practice, the bellows must always be opposed by a spring, and the deflection characteristics will be the resulting force of the spring and bellows.

16. The END